The present invention relates to a telephone control apparatus and a method for a key telephone apparatus which generates an incoming call tone in accordance with a calling signal from a private branch exchange (PBX), and to a telephone exchange apparatus and a method for accommodating a plurality of outside lines and for seizing an arbitrary outside line of the plurality of outside lines.
Conventionally, a PBX discriminates whether an incoming call is from an outside line or from an extension to call a destination extension. A key telephone connected to the PBX rings utilizing current by a calling signal from the PBX or generates an incoming call tone utilizing a power source and a sound source equipped with the telephone. The telephone slightly changes the incoming call tone so that users can discriminate whether the call is from one of the outside lines and the call is from one of the extensions, however, improved methods for generating various incoming call tones for more effective usage of telephones have been desired.
In a key telephone accommodating a plurality of outside lines, an outside line is seized from idle status by going off-hook or pressing of a speaker key. In seizing the outside line, an idle outside line is selected in the order of numbers assigned to outside line keys, or an outside line except a line which has been used at a previous call is selected. However, in such a key telephone, selection of outside line is uniform, and whether or not the outside line is being called is not considered. For this reason, trouble does occur when the user erroneously makes an outgoing call onto an outside line on which an incoming call has arrived.